The skin is formed by two layers: the epidermis and the dermis. The outermost layer is the epidermis, which is mostly formed by keratinocytes, melanocytes and Langerhans' cells, and its basic function is to retain the water of the body, act as a barrier mechanism against harmful chemical agents as well as against pathogenic organisms and carry out cell renewal processes. The innermost layer, the dermis, formed by fibroblasts, adipocytes and macrophages, is strongly bound to the epidermis through the basement membrane and contains a number of nerve endings providing the touch and temperature sensations. It also houses hair follicles, sweat glands, sebaceous glands, apocrine glands and blood vessels, and one of its main functions is to maintain the elasticity and appearance of the skin.
The dermis also includes the extracellular matrix, formed by a set of extracellular proteins (fibrous proteins, glycoproteins and proteoglycans) the key function of which is to maintain the structure of the skin and the correct functioning and development of the tissues depends on their formation and regulation being correct [Wiberg C., Klatt A. R., Wagener R., Paulsson M., Bateman J. F., Heinegard D. and Morgelin M. (2003) “Complexes of matrilin-1 and biglycan or decorin connect collagen VI microfibrils to both collagen II and aggrecan” J. Biol. Chem. 278, 37698-37704]. The two most important fibrous proteins of the extracellular matrix are collagen and elastin, responsible for the mechanical properties of tissues, such as the capacity to resist stress, compression, extensibility and torsion. Proteglycans have a structural and metabolic function, whereas glycoproteins, together with proteoglycans, serve as connecting bridges between the components of the matrix and the cells [Aumailley M. and Gayraud B. (1998) “Structure and biological activity of the extracellular matrix” J. Mol. Med. 76, 253-265; Culav E. M., Clark C. H. and Merrilees M. J. (1999) “Connective tissues: matrix composition and its relevance to physical therapy” Phys. Ther. 79, 308-319; Scott J. E. (2003) “Elasticity in extracellular matrix ‘shape modules’ of tendon, cartilage, etc. A sliding proteoglycan-filament model” J. Physiol. 553, 335-343].
Collagen
Collagens are a family of fibrous proteins of the extracellular matrix which form 25% of the total protein mass in mammals. They have been classified into more than 20 families, all of them with individual characteristics fulfilling specific functions in different tissues.
The main characteristic of collagen is its helical structure formed by the association of three polypeptide chains rich in glycine and proline. Alterations in its amino acid composition cause a dysfunction and loss of its mechanical properties [Culav E. M., Clark C. H. and Merrilees M. J. (1999) “Connective tissues: matrix composition and its relevance to physical therapy” Phys. Ther. 79, 308-319]. These polypeptide chains can be associated to one another forming fibrils having a diameter of 10-300 nm and a length of up to several hundreds of micrometers in mature tissues. These fibrils often aggregate in larger structures, such as bundles of cables, which can be seen by electron microscopy as collagen fibers with a diameter of several micrometers. This process is known as [Aumailley M. and Gayraud B. (1998) “Structure and biological activity of the extracellular matrix” J. Mol. Med. 76, 253-265]. Not all collagens have the capacity to form fibrils; only type I, II, III, V and XI collagens, which are known as fibrillar collagens.
The dermis of an adult is basically formed by type I (80-90%), III, and V fibrillar collagens. Type I collagen fibers generally have a larger diameter, a characteristic which is correlated with their capacity to support a larger mechanical load. Type II collagen plays a role in the extensibility of tissue, and over the years it is replaced by type I collagen molecules, a process which is partially responsible for mature skin being less extensible than childhood skin. Type V collagen is associated to those of type I and III by regulating the diameter of fibrils [“The Biology of the Skin”, Freinkel R. K. and Woodley D. T., eds. The Parthenon Publishing Group, 2001; Culav E. M., Clark C. H. and Merrilees M. J. (1999) “Connective tissues: matrix composition and its relevance to physical therapy” Phys. Ther. 79, 308-319].
The mutations in the collagen molecule or in the molecules involved in collagen fibrillogenesis can lead to a destructured collagen such as that found in pathologies such as the Ehlers-Danlos syndrome [Ameye L. and Young M. G. (2002) “Mice deficient in small leucine-rich proteoglycans: novel in vivo models for osteoporosis, osteoarthritis, Ehlers-Danlos syndrome, muscular dystrophy and corneal diseases” Glycobiology 12, 107R-116R]. Likewise, the prolonged exposure to UV rays can damage the architecture of collagen and cause its substitution for a less structured collagen with the subsequent thinning of the skin and formation of wrinkles, Finally, the damage to the architecture of collagen can give rise to disorganized collagen deposition during repair processes, as occurs in liver cirrhosis, pulmonary fibrosis or dermal scar formation processes. Therefore, the regulation of collagen organization can be potentially useful not only for cosmetic or dermopharmaceutical treatments but also for treating various clinical conditions.
Proteoglycans
Proteoglycans are one of the major components of the extracellular matrix and are characterized by having a protein core covalently bound to carbohydrates called glycosaminoglycans (GAGs). They are involved in many of the cell processes occurring by means of molecular interactions in the cell surface, such as cell-extracellular matrix, cell-cell and receptor-ligand interactions, since they bind avidly to proteins, and are very abundant in these regions [Perrimon N. and Bernfield M. (2001) “Cellular functions of proteoglycans—an overview” Semin. Cell Dev. Biol. 12, 65-67]. Proteoglycans act as tissue organizers, they facilitate cell growth and the maturation of specialized tissues, they play an essential role as biological filters and regulate the activity of growth factors [Iozzo R. V. (1998) “Matrix proteoglycans: from molecular design to cellular function” Annu. Rev. Biochem. 67, 609-652; Ruoslahti E. (1989) “Proteoglycans in cell regulation” J. Biol. Chem. 264, 13369-13372].
GAGs are polymers formed by disaccharide repeats, generally an acetylated amino sugar (N-acetylglucosamine or N-acetylgalactosamine) alternating with uronic acid (glucuronate or iduronate), and have a high index of sulfate groups, except hyaluronic acid. Due to their high content in acid groups, they are negatively charged and tend to attract cations such as Na+ and, as they are osmotically active, they attract water and allow maintaining tissue hydration. The commonest GAGs are hyaluronic acid, chondroitin sulfate, dermatan sulfate, heparan sulfate and keratan sulfate [Sugahara K. and Kitagawa H. (2000) “Recent advances in the study of the biosynthesis and functions of sulfated glycosaminoglycans” Curr. Opin. Struct. Biol. 10, 518-527; Zamfir A., Seidler D. G., Kresse H. and Peter-Katalinic J. (2003) “Structural investigation of chondroitin/dermatan sulfated oligosaccharides from human skin fibroblast decorin” Glycobiology 13, 733-742].
One type of proteoglycans are the so-called “leucine-rich proteoglycans”, which do not interact with hyaluronic acid and are involved in the structuring of extracellular matrices, in the modulation of the activity of growth factors as well as in the regulation of cell growth properties [Iozzo R. V. (1997) “The family of the small leucine-rich proteoglycans: key regulators of matrix assembly and cellular growth” Crit. Rev. Biochem. Mol. Biol. 32, 141-174]. Although the different leucine-rich proteoglycans have common structural characteristics, they are markedly different in their genetic regulation, in their expression pattern as well as in their functional interactions [Ramamurthy P., Hocking A. M. and McQuillan D. J. (1996) “Recombinant decorin glycoforms. Purification and structure” J. Biol. Chem. 271, 19578-19584].
The proteoglycans of the skin include versican, decorin, biglycan and hyaluronic acid. These molecules are located in specific areas of the skin. Decorin is thus in association with dermal fibers [Bianco P., Fisher L. W, Young M. F., Termine J. D. and Robey P. G. (1990) “Expression and localization of the two small proteoglycans biglycan and decorin in developing human skeletal and non-skeletal tissues” J. Histochem. Cytochem. 38, 1549-1563], biglycan is in differentiating keratinocytes in the epidermis and in the vascular endothelium [Bianco P., Fisher L. W., Young M. F., Termine J. D. and Robey P. G. (1990) “Expression and localization of the two small proteoglycans biglycan and decorin in developing human skeletal and non-skeletal tissues” J. Histochem. Cytochem. 38, 1549-1563] and versican is detected in the basal lamina of the epidermis and in association with the fibers of the elastic network of the dermis, as well as in sweat glands and in the hair follicle coating [Zimmermann D. R., Dours-Zimmermann M. T., Schubert M. and Bruckner-Tuderman L. (1994) “Versican is expressed in the proliferating zone in the epidermis and in association with the elastic network of the dermis” J. Cell Biol. 124, 817-825]. Other studies indicate that versican is not present in the epithelium of adult skin, but is present in the connective tissues adjacent to these areas, including the dermis and in the hair follicle coating [Carrino D. A., Sorrell J. M. and Caplan A. I. (2000) “Age-related changes in the proteoglycans of human skin” Arch. Biochem. Biophys. 373, 91-101].
Decorin
Decorin is considered to be one of the key proteoglycans in the regulation of the structuring and function of many elements of the extracellular matrix. Decorin binds to growth factors, including the transforming growth factor-beta (TGF-β), to other proteins of the extracellular matrix such as fibronectin and thrombospondin, to cell membrane receptors (decorin endocytosis receptor), and can also interfere directly on the cell cycle through the induction of p21, a potent cyclin-dependent kinase (CDK) inhibitor) [Stander M., Naumann U., Wick W. and Weller M. (1999) “Transforming growth factor-beta and p-21: multiple molecular targets of decorin-mediated suppression of neoplastic growth” Cell Tissue Res. 296, 221-227].
Many of the studies on the interaction of decorin are about the binding to type I collagen, although it is known that they also interact with other collagens such as types II, III and VI collagens. Although it is considered that the main factor affecting the formation of collagen fibrils in vivo is the actual structure of collagen, there are different molecules such as decorin which can regulate and adjust this process. Decorin delays the formation of fibrils and makes it difficult, it causes a consequent reduction in the average diameters of the fibrils and forces collagen fibers to adopt a regular spatial distribution [Danielson K. G., Fazzio A., Cohen I., Cannizzaro L. A., Eichstetter L. and Iozzo R. V. (1993) “The human decorin gene: intron-exon organization, discovery of two alternatively spliced exons in the 5′ untranslated region, and mapping of the gene to chromosome 12q23” Genomics 15, 146-160]. This process is mediated by the protein core of the proteoglycan, and requires it to conserve its tertiary structure [Svensson L., Heinegard D. and Oldberg A. (1995) “Decorin-binding sites for collagen type I are mainly located in leucine-rich repeats 4-5” J. Biol. Chem. 270, 20712-20716; Keene D. R., Ridgway C. C. and Iozzo R. V. (1998) “Type VI microfilaments interact with a specific region of banded collagen fibrils in skin” J. Histochem. Cytochem. 46, 215-220]. There is evidence that the triple helix of type I collagen has a specific decorin-binding site [Keene D. R., Ridgway C. C. and Iozzo R. V. (1998) “Type VI microfilaments interact with a specific region of banded collagen fibrils in skin” J. Histochem. Cytochem. 46, 215-220] and that there are additional interactions with dermatan sulfate molecules [Kresse H., Liszio C., Schonherr E. and Fisher L. W. (1997) “Critical role of glutamate in a central leucine-rich repeat of decorin for interaction with type I collagen” J. Biol. Chem. 272, 18404-18410]. Decorin binds to two adjacent parallel collagen molecules of the fibril, aiding in stabilizing the fibril and orienting fibrillogenesis. As it is bound to the collagen fibril surface, the lateral interaction between the triple helixes of collagen becomes more difficult, since it acts as a spacer and the diameter of the fibrils decreases, thus controlling the dimensions of the fibrils, specifically the uniformity of their diameter and the regular distance between them, thus allowing it to maintain the shape of the tissue [Tenni R., Viola M., Welser F., Sini P., Giudici C., Rossi A. and Tira M. E. (2002) “Interaction of decorin with CNBr peptides from collagens I and II. Evidence for multiple binding sites and essential lysyl residues in collagen” Eur. J. Biochem. 269, 1428-1437; Scott J. E. (1996) “Proteodermatan and proteokeratan sulfate (decorin, lumican/fibromodulin) proteins are horseshoe shaped. Implications for their interactions with collagen” Biochemistry 35, 8795-8799].
The importance of these interactions of decorin with collagen has also been demonstrated in vivo by means of the transgenic mice which do not have the decorin gene and therefore do not produce decorin in their organism. These animals are viable but have a very fragile skin, with a very thin dermis, with a reduced elastic strength and reduced tensile strength, and their histopathological analysis shows that their collagen fibrils have irregular diameters along the fibrils due to uncontrolled lateral aggregations [Kresse H., Liszio C., Schonherr E. and Fisher L. W. (1997) “Critical role of glutamate in a central leucine-rich repeat of decorin for interaction with type I collagen” J. Biol. Chem. 272, 18404-18410; Danielson K. G., Baribault H., Holmes D. F., Graham H., Kadler K. E. and Iozzo R. V (1997) “Targeted disruption of decorin leads to abnormal collagen fibril morphology and skin fragility” J. Cell. Biol. 136, 729-743; Keene D. R., Ridgway C. C. and Iozzo R. V. (1998) “Type VI microfilaments interact with a specific region of banded collagen fibrils in skin” J. Histochem. Cytochem. 46, 215-220]. This observation is consistent with the widely accepted fact that the strength of the skin is directly correlated with the general organization, the content and the physical properties of the fibrillar collagen network [Dombi G. W., Haut R. C. and Sullivan W. G. (1993) “Correlation of high-speed tensile strength with collagen content in control and lathyritic rat skin” J. Surg. Res. 54, 21-28]. Furthermore, said transgenic animals also have an increased collagen degradation, which contributes to their poor skin quality [Schaefer L., Macakova K., Raslik I., Micegova M., Gröne H-J., Schönherr E., Robenek H., Echtermeyer F. G., Grässel S., Bruckner P., Schaefer R. M., Iozzo R. V. and Kresse H. (2002) “Absence of decorin adversely influences tubulointerstitial fibrosis of the obstructed kidney by enhanced apoptosis and increased inflammatory reaction” Am. J. Pathol. 160, 1181-1191]. An irregular organization of collagen fibrils in different human pathologies leading to phenotypes with fragile skin can also be observed, suggesting that the alteration of fibrillogenesis processes is enough to cause a fragile skin and a disorganized structure of the matrix, and consequently the individuals having a deregulated fibrillogenesis process have a higher incidence of injuries as well as of abnormal healing processes [Keene D. R., Ridgway C. C. and Iozzo R. V. (1998) “Type VI microfilaments interact with a specific region of banded collagen fibrils in skin” J. Histochem. Cytochem. 46, 215-220; Iozzo R. V. (1999) “The biology of the small leucine-rich proteoglycans” J. Biol. Chem. 274, 18843-18846].
Decorin not only interacts with collagen fibers, but also interacts with other structural proteins. This is presumably due to its horseshoe shaped three-dimensional structure, where the leucine-rich region repeats are arranged in parallel, only a few repeats being necessary for its binding to a ligand [Schonherr E., Broszat M., Brandan E., Bruckner P. and Kresse H. (1998) “Decorin core protein fragment Leu155-Val260 interacts with TGF-beta but does not compete for decorin binding to type I collagen” Arch. Biochem. Biophys. 355, 241-248]. From the results of molecular dynamics studies conducted it is inferred that the concave face of the decorin horseshoe has an opening with an angle sufficient to accommodate a triple helix, with a diameter of approximately 2 nm, which is slightly greater than the diameter of a collagen (1.5 nm), whereas the arms of the horseshoe have a thickness similar to the collagen molecule [Kresse H., Liszio C., Schonherr E. and Fisher L. W. (1997) “Critical role of glutamate in a central leucine-rich repeat of decorin for interaction with type I collagen” J. Biol. Chem. 272, 18404-18410; Scott J. E. (1996) “Proteodermatan and proteokeratan sulfate (decorin, lumican/fibromodulin) proteins are horseshoe shaped. Implications for their interactions with collagen” Biochemistry 35, 8795-8799].
The theoretical structural studies conducted consider the hypothesis that the Lys130-Arg133 and Arg272-His275 decorin regions are responsible for the binding to collagen, specifically the Asp857-Arg-Gly-Glu860 region [Kresse H., Liszio C., Schonherr E. and Fisher L. W. (1997) “Critical role of glutamate in a central leucine-rich repeat of decorin for interaction with type I collagen” J. Biol. Chem. 272, 18404-18410]. The two decorin regions are one in each arm of the horseshoe, approximately equidistant from the ends of the molecule, in an anti-parallel direction. However, the fact that decorin adopts a horseshoe shape makes the linear sequence rotate 180° of one arm of the horseshoe to the other arm, the two fragments actually being in a parallel arrangement. A complementarity of the charges of the side-chain residues involved in the interaction ([−,+,0,−] for collagen and [+,−,0,+] for the decorin fragments) is thus achieved, which seems to be critical for stabilizing the interaction between the two molecules [Scott J. E. (1996) “Proteodermatan and proteokeratan sulfate (decorin, lumican/fibromodulin) proteins are horseshoe shaped. Implications for their interactions with collagen” Biochemistry 35, 8795-8799].
Aging
The skin undergoes dramatic changes with age, including changes in its morphology, physiology and in its mechanical properties. The skin of babies is smooth and soft, with a thick layer of fat and a very thin protective layer of keratin, where the skin of the elderly is very thin and has many wrinkles, with a very small layer of fat. The extracellular matrix also experiences changes with age, and these contribute to the group of changes of the physical properties of the skin related to aging [Wiberg C., Klatt A. R., Wagener R., Paulsson M., Bateman J. F., Heinegard D. and Morgelin M. (2003) “Complexes of matrilin-1 and biglycan or decorin connect collagen VI microfibrils to both collagen II and aggrecan” J. Biol. Chem. 278, 37698-37704]. The prolonged exposure to the sun and the environmental contaminants accelerate the skin aging process since the exposure to UV rays inhibits the synthesis of collagen and fibronectin in fibroblasts and catalyzes collagen degradation by stimulating the synthesis of the enzymes degrading it (matrix metalloproteases). Changes in type I collagen molecules, which are the major components of the extracellular matrix of the dermis, have been described [Hunzelmann N., Ueberham U., Eckes B., Hermann K. and Krieg T. (1997) “Transforming growth factor-beta reverses deficient expression of type (I) collagen in cultured fibroblasts of a patient with metageria” Biochim. Biophys. Acta. 1360, 64-70].
The cosmetic industry has made important efforts to counteract this loss of functionality of the components of the extracellular matrix with age. The balance between the production and the degradation of essential biomolecules of the skin (collagen, for example) tends, with aging, towards degradation processes, and this leads to a progressive thinning and disorganization of the dermis causing flaccidity in the dermis with the subsequent formation of wrinkles. At a microscopic level, the collagen of aged skin (both chronologically aged skin—mature skin—and skin aged by prolonged exposure to the sun or to environmental contaminants) is characterized by having thick fibrils organized in a manner similar to bundles of cables, which are not as aligned as in young skin [Oikarinen A. (1990) “The aging of the skin: chronoaging versus photoaging” Photodermatol. Photoimmunol. Photomed. 7, 3-4]. Therefore, the methods allowing a better organization of collagen fibers will have a potential beneficial effect on mature skin or on aged skin, allowing it to partially recover the mechanical properties (elasticity, flexibility and firmness) lost with age or exposure to the sun and/or to environmental contaminants and having a better appearance, with less presence of wrinkles and smoother.
In addition to collagen, the dermal extracellular matrix also contains proteoglycans which are involved in the properties of tissues and are altered with aging. Among them, decorin is catabolized into a fragment which is known as decorunt, corresponding to a version of decorin which lacks the carboxy-terminal fragment. The skin with a fetal origin do not, however, have detectable decorunt levels, whereas the maximum decorunt levels are determined from 30 years onwards, which is the age from which aging signs start to be manifested. The capacity of decorunt to bind to a collagen molecule is 100 times less than of decorin alone, a factor which is correlated to the fact that decorunt precisely lacks one of the decorin regions which is essential for the binding to collagen [Wiberg C., Klatt A. R., Wagener R., Paulsson M., Bateman J. F., Heinegard D. and Morgelin M. (2003) “Complexes of matrilin-1 and biglycan or decorin connect collagen VI microfibrils to both collagen II and aggrecan” J. Biol. Chem. 278, 37698-37704]. Knowing that decorin affects collagen fibrillogenesis processes and regulates the diameter of fibrils, the appearance of decorunt can have an important effect on the elasticity and morphological differences between the collagen fibers of young skin and those of aged skin [Carrino D. A., Sorrell J. M. and Caplan A. I. (2000) “Age-related changes in the proteoglycans of human skin” Arch. Biochem. Biophys. 373, 91-101]. It has also been demonstrated that the synthesis of decorin is reduced in skin aged by prolonged exposure to the sun or to environmental contaminants [Bernstein E. F., Fisher L. W., Li K., LeBaron R. G., Tan E. M. and Uitto J. (1995) “Differential expression of the versican and decorin genes in photoaged and sun-protected skin. Comparison by immunohistochemical and northern analyses” Lab. Invest. 72, 662-669], therefore this type of skin has a disorganization of collagen. Therefore, the decrease of the functional decorin content of aged skin, either due to age or due to prolonged exposure to the sun and to environmental contaminants, is directly related to the formation of a destructured fibrillar collagen network leading to a skin which is fragile, less elastic and with less tensile strength.
Healing
Wound healing in adults is a complicated reparative process. The healing process starts with the recruitment of a variety of specialized cells for their transfer to the wound site, and involves extracellular matrix and basement membrane deposition, angiogenesis, selective protease activity and re-epithelization. An important component of the healing process in adult mammals is fibroblast stimulation to generate the extracellular matrix. This extracellular matrix is a main component of the connective tissue which is developed to repair the wound area.
The connective tissue which is formed during the healing process often has a fibrous nature. A scar is an abnormal morphological structure resulting from a previous injury or wound (such as, for example, an incision, an excision or a trauma) and is formed by a connective tissue which is predominantly a type I and II collagen matrix and fibronectin. In the skin, the scar consists of collagen fibers in an abnormal organization as well as of an excess collagen deposition. In mammals, when the scar is raised above the skin, having a bulging appearance, it is due to the fact that they contain excess collagen arranged in an irregular manner, and are classified as hypertrophic scars. A keloid is another form of pathological scarring which is not only raised above the surface of the skin, but also extends to beyond the limits of the original injury, and it also has an excessive amount of connective tissue which is organized in an abnormal manner, predominantly forming vortical bands of connective tissue. An analysis of the decorin content in hypertrophic scars shows that its concentration is only 25% of that found in healthy tissues [Scott P. G., Dodd C. M., Ghahary A., Shen J. and Tredget E. E. (1998) “Fibroblasts from post-burn hypertrophic scar tissue synthesize less decorin than normal dermal fibroblasts” Clin. Sci. (Lond). 94, 541-547], a fact which explains the irregular organization of the collagen present in hypertrophic scars.
Likewise, truncated forms of decorin have been detected in hypertrophic scars [Honda T., Matsunaga E., Katagiri K., and Shinkai H. (1986) “The proteoglycans in hypertrophic scar” J. Dermatol. 13, 326-333; Garg H. G., Lippay E. W, Burd D. A. R and Neame P. J. (1990) “Purification and characterization of iduronic acid-rich and glucuronic acid-rich proteoglycans implicated in human post-burn keloid scar” Carbohydr. Res. 207, 295-305], and it has been demonstrated that these truncated forms are not capable of regulating the formation of collagen fibrils in a fibrillogenesis assay [Carrino D. A., Önnerfjord P., Sandy J. D., CS-Szabo G., Scott P. G., Sorrell J. M., Heinegard D. and Caplan A. I. (2003) “Age related changes in the proteoglycans of human skin” J. Biol. Chem. 278, 17566-17572].
The presence of scars in the skin is a factor which is not aesthetically accepted by most human beings. The medical sector has made important efforts to develop minimally invasive surgical process, such as arthroscopies or laparoscopies, which not only decrease the risks of post-surgical complications but also have the advantage of leaving scars of very small sizes or hardly visible scars. Despite these efforts, most surgical interventions are still carried out by open surgery, such that the control of the correct healing process is still an extremely important issue. Preventing the formation of hypertrophic scars and/or keloids, which have an irregularly organized collagen, is one of the objectives of the cosmetic and dermopharmaceutical sector. Therefore, the methods allowing a better organization of collagen fibers will have a potential beneficial effect on scars, allowing them to soften their appearance.
Therefore, the cosmetic or dermopharmaceutical compositions containing molecules imitating the activity of decorin by interacting with collagen fibrils or fibers, regulating the fibrillogenesis process, are potential candidates for their use as anti-aging products for the purpose of increasing the elasticity, firmness, structuring and flexibility of the skin, or as coadjuvants in post-surgical treatments for the purpose of softening the appearance of scars.
There are different patents with a cosmetic or dermopharmaceutical application which mention decorin for the treatment or prevention of aging, as well as for softening the appearance of scars. Patent application US2003/0124152 describes the use of decorin in cosmetic or dermatological compositions for the treatment of intrinsic (due to the passage of time and to genetic factors) or extrinsic (due to prolonged exposure to the sun or to environmental factors such as ultraviolet (UV) radiation, chemical contaminants, cigarette smoke and pollution) aging. U.S. Pat. No. 5,510,328 describes the use of decorin in pharmaceutical compositions for reducing or inhibiting wound contraction, and U.S. Pat. No. 6,509,314 describes the use of decorin for preventing or reducing wound scarring. There are other patents describing plant extracts or compounds which stimulate the synthesis of endogenous decorin, such as, for example, those described in patents JP2004051508, FR2834462, EP1367988, U.S. Pat. No. 6,551,602, U.S. Pat. No. 6,455,057, U.S. Pat. No. 6,440,434, U.S. Pat. No. 6,423,325, U.S. Pat. No. 6,287,553 and U.S. Pat. No. 6,042,841. Research works focused on the search for the domains of decorin binding to collagen have been published in the literature which describe some synthetic peptides which are capable of binding to collagen, and which could potentially have the same activity as decorin, but all the sequences correspond to native decorin fragments [Vides V. M., Laschinger C. A., Arora P. D., Lee W, Hakkinen L., Larjava H., Sodek J. and McCulloch C. A. (2005) “Collagen phagocytosis by fibroblasts is regulated by decorin” J. Biol. Chem. 280, 23103-23113; Schonherr E., Broszat M., Brandan E., Bruckner P. and Kresse H. (1998) “Decorin core protein fragment Leu155-Val260 interacts with TGF-beta but does not compete for decorin binding to type I collagen” Arch. Biochem. Biophys. 355, 241-248]. However, there is currently no reference to the use of peptides not contained in the native decorin sequence which imitate the action of decorin in its binding to collagen, regulating fibrillogenesis and aiding in maintaining a structured collagen network.
The applicant of the present invention has determined that the synthetic peptides of the invention are effective in regulating fibrillogenesis, thus imitating the function of decorin. The sequence of the peptides of the invention is not contained in the native decorin sequence, therefore they can be considered as peptide mimetics of the activity of decorin. It has been postulated in the literature that for their binding to collagen, and consequently the regulation of fibrillogenesis, the peptide sequences must have four amino acids with a [+,−,0,+] charge pattern [Scott J. E. (1996) “Proteodermatan and proteokeratan sulfate (decorin, lumican/fibromodulin) proteins are horseshoe shaped. Implications for their interactions with collagen” Biochemistry 35, 8795-8799], such that there is a charge complementarity with the Asp857-Arg-Gly-Glu860 collagen fragment which allows stabilizing the interaction. The applicant of the present invention has determined that not all the sequences complying said charge complementarity postulated by Scott are capable of regulating fibrillogenesis. While the synthetic peptide RELH, corresponding to the decorin sequence 272-275 complies with the charge pattern and is capable of regulating fibrillogenesis, peptides His-Asp-Ala-Arg, Orn-Asp-Nva-His, His-Asp-Ile-His also comply with the charge pattern but have no effect on fibrillogenesis. Therefore, the compliance with the [+,−,0,+] charge pattern postulated by Scott is not a sufficient requirement for the regulation of fibrillogenesis by the peptides complying with it. The studies conducted by the applicant of the present invention have surprisingly established that the regulation of fibrillogenesis is determined by the peptide sequences having a citrulline amino acid residue together with a [+,−,0] charge pattern, such as, for example, the sequences Lys-Asp-Ile-Cit or Lys-Asp-Val-Cit. Patent RU2,181,728 describes a synthetic peptide of 10 amino acids bound by means of a disulfide bond to a peptide of 12 amino acids having a sequence including the sequence Lys-Glu-Leu-Cit, which is based on the interleukin-8 molecule and stimulates the migration of neutrophils. Despite the fact that said peptide complies with the [+,−,0] charge pattern and has a contiguous citrulline residue, it is not included within the family of the peptides of the present invention since it has a total of 22 amino acids. Furthermore, said patent does not give any indication nor suggest that the peptide described is capable of inhibiting fibrillogenesis.
Therefore, there is no indication in the state of the art that citrulline is a necessary residue for the regulation of fibrillogenesis, therefore a person skilled in the art could not deduce the nature of the peptides regulating fibrillogenesis.
Therefore, the peptides of the present invention can be useful in the treatment of the skin conditions requiring a regulation of fibrillogenesis, such as the treatment of aged skin (either due to age or due to exposure to the sun and/or to environmental contaminants) or as coadjuvants in healing processes to soften the appearance of scars.